Twenty years after the first Earth summit in Rio, there is a growing recognition that unless countries actually deliver on the promises they make at great events such as Rio+20, their words – as St Paul put it – may be as "sounding brass and tinkling cymbals".

Civil society in its numerous forms is determined to make its voice heard at side-events in Rio. Twenty years ago a group of Yanomami Indians, all sporting their distinctive lip-stretching bangles, gripped the attention of the conference with their plea for the rights of indigenous peoples.

The most important side-event in 2012 may be the first-ever gathering of the chief justices of the world's supreme courts – the Unep-organised World Congress on Justice, Law and Environmental Sustainability.

Supreme court justices from all over the world (including the UK) met on Sunday night in the splendour of Rio de Janeiro's own Tribunal di Justiça to make it absolutely clear that environmental rights were part and parcel of the rule of law, to be enforced alongside, and indeed as a component of, basic human rights.

One of the most remarkable speeches was given by Ricardo Lorenzetti, the supreme court chief justice of Argentina. He made it absolutely clear that in his view it was the duty of the judiciary to stop the politicians reneging on their promises, or the "no-regression principle". Once a human right has been admitted, including the right to a decent environment, it cannot be reversed. "The key role of the judiciary is that we do not depend on election," he said.

Mr Kwon Jae-Jin, Korea's minister of justice, gave a graphic account of how his country had cleaned up the rivers and waterways by using the full force of the law against polluting industries.

Prof Nicholas Robinson, a former chairman of IUCN's Commission on Environmental Law, said: "It is probably utopic to expect that judges by themselves will be able to solve the environmental problems of the planet. But too bad for the planet if it doesn't have the judges on its side."

Achim Steiner, Unep's executive director, told the gathering that good governance nationally as well as internationally was one of the key themes at Rio+20. "Citizens have to be able to take their own governments to account for failure to uphold commitments they have entered into," Steiner said.

The present draft of Our Common Vision, part of the overall text negotiators in Rio are working on, states: "We encourage action at regional, national, sub-national, and local levels to promote access to information, public participation, and access to justice in environmental matters, as appropriate." The chief justices of the world's supreme courts, assembled in their own congress in Rio this week, will be working hard behind the scenes to ensure that its language is not watered down any further.

• Stanley Johnson's new book: Where the Wild Things Were: Travels of a Conservationist will be published by Stacey International in July